Studies are being done to characterize the process of membrane fusion involved in the liver heterophagy of serum asialo-glycoproteins. The fusion process involves the membranes of phagosomes and lysosomes to yield phagolysosomes(secondary lysosomes), a cellular compartment which contains both endocytized glycoproteins and lysosomal hydrolases. In order to isolate phagosomes, a perfused liver will be treated with drugs affecting microtubules such as colchicine, vinblastine and cytocholasin B. In a liver provided with asialo-glycoprotein it is expected that some of these compounds will allow phagocytosis to continue, but fusion will be prevented, and thereby a large number of phagosomes will accummulate. Isolation of these structures from the treated livers will be done by density gradient centrifugation techniques. Finally the phagosome membrane will be purified from the disrupted organelles and their biochemical properties measured. The proteins and glycoproteins of the lysosomal membrane also will be located on the external organelle surface by lactoperoxidase iodination of intact Triton WR-1339 filled lysosomes. The iodinated membranes will be isolated and after their solubilization, subjected to SDS-gel electrophoresis. Radioactive peptides will be noted and in addition specific carbohydrate residues on the separated proteins will be located by precipitation with various plant lectins. In other experiments the lysosomal accumulation (purified beef spleen) beta-D-hexosaminidase B will be measured after adding the enzyme to a perfused rat liver system. BIBLIOGRAPHIC REFERENCES: Catabolism of Methylated and Iodinated Asialo-fetuin in the Rat. LaBadie, J.H., Chapman, K.P. and Aronson, Jr., N.W., Fed. Proc. 34, 687 Abst. (1975). Glycoprotein Catabolism in Rat Liver. Lysosomal Digestion of Iodinated Asialo-fetuin. LaBadie, J.H., Chapman, K.P. and Aronson, Jr., N.N., Biochem. J. 152, 271-279 (1975).